The present invention relates generally to industrial robots and more particularly to an industrial robot wherein, for workpieces which are transfered in succession by a conveyor system, operation or working is carried out in accordance with contents memorized in a memory apparatus.
In general, the playback type industrial robot is so adapted that the moving or displacing operation of a movable part may be memorized or taught in the memory apparatus by moving manually the movable part by an operator, and that, in a playback operation mode, the movable part operates or moves automatically in accordance with the memorized or taught contents. Accordingly, the playback type industrial robot is not necessitated to arrange a working program through the use of devices such as a pin-board. Therefore, the robot of this type has the advantage that the working contents can be easily and accurately memorized or preset.
In the case of applying industrial robots of this type to an apparatus for spray-painting a workpiece conveyed or transferred in succession along a conveyor line, for instance, an operator manipulates, in teaching mode, to move an arm of a robot structure in accordance with actual motion of the workpiece and to spray paint by means of a spray gun provided at a distal end of the arm onto the workpiece. The motion of the arm is detected by an arm position detection means, and then memorized in a memory apparatus in a control board unit.
The industrial robot known heretofore is adapted so that, whereupon a teaching operator closes a switch on the arm at a time instant when he judges that the workpiece reaches a predetermined operating place, the memory apparatus turns to a state of capable of memorizing, and whereby the motion of arm hereinafter is memorized. In a case where the speed of the conveyor line changes due to voltage fluctuation and the like, there occur an instance wherein playback operation is not carried out at a position, with respect to the workpiece, where the teaching operation is conducted by the operator. Accordingly, the time instant of initiating playback operation is sometimes deviated from the time instant of initiating teaching operation, which results in difficulty that uneveness of painting takes place in the workpiece.
This difficulty may be eliminated by providing a delay circuit in a control board unit, for example. The delay circuit causes the signal from the detection switch to delay by a specific period of time so that the starting timing of play-back operation comes to coincide with that of teaching. This arrangement, however, involves difficulties such that setting of delay time in the delay circuit must be carried out in a try-and-error manner, and that adjustment of delay time is required every time when the conveying speed of the conveyor line is changed. This change of conveying speed must be made, for instance, when the working advancing degree in the following process is taken into consideration.
Moreover, the industrial robot of the above described structure is generally arranged, in view of the fact that conveying speed of the conveyor sometimes changes depending on working speeds at process stages preceding to and succeeding to the painting process, for instance, so that the operation speed of the robot structure can be variably changed by manipulating an adjusting knob, such as a volume knob, provided on the control board unit. This industrial robot is, however, accompanied with difficulties such that the operation speed of the robot structure, which is adjusted by the operator, is hardly synchronized with the conveying speed of the conveyor line, and that, even if the operation speed is adjusted accurately, any deviation in speed of the conveyor line due to change in workpiece weight may sometimes result in that the robot structure operates for the imaginary workpiece, not for the actual workpiece to which the spray-painting should be applied.
There have been instances wherein a plurality of different types of workpieces with different shapes and sizes is spray-painted through the use of the same industrial robot. A program presetting device of pin-board type is often employed in such cases, and arrangement of pins on the board is required to change in accordance with kinds of workpieces. Accordingly, particularly in a case such as that where a number of kinds of workpieces is large and a number of workpieces is large and a number of workpieces of the same type is small, or where the conveying speed of the conveyor line is relatively high, there arise difficulties that manipulation of changing arrangement of pin becomes much troublesome.